Touch panels are touch-sensing input apparatuses, which are widely used. The most commonly known types of touch panels include resistive touch panels, capacitive touch panels, surface infrared touch panels, and the like according to the principle of touch sensing. The resistive touch panel has been popular for years due to its advantages of low cost, easy implementation and simple control. In recent years, the capacitive touch panel becomes popular because it has high light transmittance, good abrasion resistance, good resistance to environmental variations in temperature and humidity, long operating life, and advanced and complex functions such as multi touch capability.
Integrating the touch panel as a graphical user interface into a display device such as an LCD screen is well-known. Traditionally, the touch panel is adhered externally to the display screen. In this case, the touch panel and the display screen are fabricated separately and then assembled together. As shown in FIG. 1, a touch panel 10 includes a first protection layer 11, a second protection layer 13 and a touch layer 12 located between the first protection layer 11 and the second protection layer 13. The first protection layer 11 and the second protection layer 13 may be glass or special material films. The first protection layer 11 is disposed at the outside of the touch panel 10, and the second protection layer 13 is disposed close to the display screen 20. The display screen 20 includes an upper glass substrate 21 and a lower glass substrate 22. A black matrix layer 23, a color filter layer 24, a common electrode layer 25, a liquid crystal layer 26 and a thin film transistor (abbreviated as TFT) layer 27 are formed sequentially between the upper glass substrate 21 and the lower glass substrate 22. The touch panel 10 is an outboard touch panel, and the display screen 20 has poor optical performance due to the complex structure and large thickness of the touch panel 10.
In order to reduce the thickness of the whole module and improve the optical performance, the way for integrating the touch panel is directly integrated into the display screen directly (i.e., the touch panel and the display screen are manufactured simultaneously) has aroused more and more concern. In this way, the touch panel structure is fabricated in the upper glass substrate of the LCD screen. A touch panel includes an on-cell touch panel (on-cell TP) and an in-cell touch panel (in-cell TP) according to integrating manner.
For the on cell touch panel, the touch panel is integrated into the outside surface of the upper glass substrate of the display screen, that is, the upper glass substrate of the display screen is also used as the lower protection layer of the touch panel. As shown in FIG. 2, a touch panel 30 includes a protection layer 31 and a touch layer 32 below the protection layer 31, and the protection layer 31 is placed outside the touch panel. A display screen 40 includes an upper glass substrate 41 and a lower glass substrate 42. A black matrix layer 43, a color filter layer 44, a common electrode layer 45, a liquid crystal layer 46 and a thin film transistor (abbreviated as TFT) layer 47 are formed sequentially between the upper glass substrate 41 and the lower glass substrate 42.
For the in-cell touch panel, the touch panel structure is completely integrated into the liquid crystal screen. As shown in FIG. 3, the in-cell touch panel LCD module includes an upper glass substrate 51; a lower glass substrate 52; and a touch layer 53, a black matrix layer 54, a color filter layer 55, a common electrode layer 56, a liquid crystal layer 57 and a TFT layer 58 formed sequentially between the upper glass substrate 51 and the lower glass substrate 52.
The touch layer in the on cell touch panel and the in-cell touch panel includes multiple parallel driving lines extending in an X direction and multiple parallel sensing lines extending in a Y direction, and the driving lines cross the sensing lines. The detection principle of the touch panel will be described briefly: When a driving signal is applied to the driving line and a signal change is detected on the sensing line. The driving line is used to determine the coordinate in the X direction of the touch point, and the sensing line is used to determine the coordinate in the Y direction of the touch point. In detecting, the driving lines in the X direction are scanned line by line and the signal on each sensing line is read during the scanning, thus each of crossings of the driving lines and the sensing lines may be traversed by one cycle of scanning. Therefore, the location corresponding to the touch action is determined. An equivalent circuit diagram of a crossing of a driving line and a sensing line is shown in FIG. 4. A mutual capacitance 61 is formed at each crossing, and the mutual capacitance 61 is equal to a sum of a right opposite capacitance formed at the position at which the driving line is right opposite to the sensing line and an edge capacitance formed at the edge positions of the driving line and the sensing line. An equivalent resistance of the driving line is defined as resistance 62, and an equivalent resistance of the sensing line is defined as resistance 63. Capacitance 64 is equivalent to a parasitic capacitance of the driving line with respect to the ground, and capacitance 65 is equivalent to a parasitic capacitance of the sensing line with respect to the ground. An excitation source 66 generates a drive signal. A touch control detection circuit 67 is an amplifier which converts an electric signal on the sensing line into an output voltage signal Vout. When the touch panel is touched by a finger, a bridge is built between the driving line and the sensing line at the touch location as the finger is an electrical conductor, that is, a capacitor is connected with the mutual capacitance 61 in parallel, therefore, the value of equivalent mutual capacitance 61 is increased, which causes a change in and electric signal on the sensing line, and accordingly, a change of the output voltage Vout.
The on-cell touch panel has the advantage of small noise interference, but also has complex production process and low yield compared with the in-cell touch panel. Therefore, the in-cell touch panel is mostly widely employed. However, the touch layer is very close to the common electrode layer in the existing in-cell capacitive touch panel LCD apparatus, and the touch panel is sensing the touch control signal from the user while the LCD screen is displaying images frame by frame, therefore, the touch panel is likely be affected by the electrical noise generated by the LCD screen, leading to a low signal-to-noise ratio of the touch panel.